Investigating Symmetry in Crystals
Observing Identifying Factors that Influence Crystal Growth
Feb 14, 2009
Most minerals occur naturally as crystals, which are non-organic or not living objects. Every crystal has an orderly internal pattern of atoms, with a distinctive way of locking new atoms into a pattern that repeats again and again. This is called symmetry, a regular repeated pattern of component parts. The shape of a crystal, such as a cube (like salt) or a six-sided form (like a snowflake) mirrors the internal arrangement of the atoms.
As crystals grow, differences in temperature and chemical composition cause variations. The internal arrangement of atoms determines all the mineral's chemical and physical properties, including color. Light interacts with different atoms to create different colors. Many minerals are colorless in their pure state; however, impurities of the atomic structure cause color. Each crystal starts small and grows as more atoms are added. Many grow from water rich in dissolved minerals, but they also grow from melted rock and even vapor.
Growing and Investigation of Crystals
Materials (per group)
- Three shallow bowls (such as Petri dishes)
- One small clean rock
- One miscellaneous object (such as a nail, aluminum foil, shell, or marble)
- One 250 ML beaker
- Magnifying glass or microscope
- Food coloring
- Flashlight
- Scale
Teacher Materials
- Epsom salts (not table salt, but crystals of hydrated magnesium sulfate available at most pharmacies)
- Stirrer
- Water
- Hot plate
- Pan for heating water Epson salt solution
- Digital Camera(s) – see using digital cameras for investigating science for creative ideas
Procedures
- Number each bowl 1, 2, and 3
- Place a small rock in one small bowl 1, a miscellaneous item in bowl 2, and leave bowl 3 empty.
- Add Epson salt and water solution to each bowl (obtained from teacher), so that objects in bowls 1 and 2 are covered. Add the same amount of solution to each bowl. Use the beaker to measure the solution added to each bowl.
- Add two drops of food coloring in the center of each bowl. Use the same color for each bowl.
- Record your group’s observations each bowl and its contents.
- Even numbered groups place their bowls in a cool part of the classroom, while odd numbered groups place their bowls in a warm part of the classroom.
Observations of Crystals
- Make daily observations and record all data collected – such as the weight of each growing crystal; view crystals with magnifying glass or microscope to make sketches of each crystal; take pictures with a digital camera and save.
- Continue making observations a collecting data for one week.
- Prepare a multimedia presentation to share group’s findings and conclusions with the class.
- Teachers visit science projects using multimedia resources and reasons for students’ integration of technology in science projects.
Asking Students Questions
- Do the crystals have any similarities in terms of shape and symmetry when observed under the microscope or with a magnifying glass?
- How many sides (faces) does each of the crystals have?
- Does shining a flashlight on the surface of the crystals affect their appearance?
- When did the crystals stop growing? Did some stop growing before others?
- Did temperature affect the rate of crystal growth or the size of the crystals? Were warm or cold temperatures more favorable?
- How did the crystals "use" the food coloring? Did the food coloring affect the rate or size of crystal growth?
- Did crystals grow in all the bowls? If not, what may be some of the reasons why the crystals did not grow?
- Did crystals appear to grow more easily on rocks or metal? On smooth or rough objects?
Visit 20 questions to ask students in science projects for additional ideas for questions to guide discussion.
Making Connections in Inquiry-Based Science
This investigation generates a number of questions about crystal growth for students. There may not be an easy answer for every inquiry; the important thing is that the students learn to ask good questions. Inquiry based science requires students’ use a hands-on, minds-on approach to science investigations. This enables students’ to use critical thinking skills to develop and find answers to difficult questions. The investigation of symmetry in crystals involves student inquiry, science process skills, technology, and problem solving.
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